The present invention relates to novel transition metal complexes of the formula (I)
to a process for preparing these transition metal complexes and to the use of the transition metal complexes as catalysts in metathesis reactions.
Metathesis is understood to mean a chemical reaction in which formal substituents on double or triple bonds are exchanged. The metathesis reactions include the oligomerization and polymerization of acyclic dienes (ADMET) or polymerization of cyclic olefins (ROMP), and also the synthesis of cyclic compounds of different sizes by ring-closing metathesis (RCM). In addition, crossed metatheses of different alkenes (CM) and metathesis of alkenes with alkynes (ene-yne metathesis) are known. Numerous fundamental studies have contributed significantly to the understanding of this transition metal-catalysed reaction (for an overview see: Handbook of Metathesis, Ed. R. H. Grubbs, WILEY-VCH, Weinheim, 2003).
For olefin metathesis, a multitude of catalyst systems is available. Especially studies by Schrock introduced alkylidene complexes of molybdenum and of tungsten as the first well-defined catalysts (J. S. Murdzek, R. R. Schrock, Organometallics, 1987, 6, 1373-1374). However, a disadvantage was found to be the high sensitivity of these complexes. In recent times, ruthenium-alkylidene complexes with phosphine ligands have become established (P. Schwab et al. Angew. Chem. Int. Ed. Engl. 1995, 34, 2039-2041; P. A. van der Schaaf et al. J. Organometallic Chem. 2000, 606, 65-74). These complexes possess a high tolerance toward polar functional groups and are air- and water-stable. The introduction of N-heterocyclic carbenes (NHC) as ligands allowed not only the activity of these systems to be enhanced further, but also, owing to the significant variability of the ligand sphere, made available new kinds of control means for the reactions (DE 19815275 and T. Weskamp, W. C. Schattenmann, M. Spiegler, W. A. Herrmann Angew. Chem. 1998, 110, 263-2633). A further significant increase in the catalytic activity is achieved by supplementation with a more coordinatively labile ligand (DE 19902439 and T. Weskamp, F. J. Kohl, W. Hieringer, D. Gleich, W. A. Herrmann Angew. Chem., 1999, 111, 2573-2576).
Representative examples are the complexes A and B.

Gessler et al. (Tetrahedron Lett. 2000, 41, 9973-9976) and Garber et al. (J. Am. Chem. Soc. 2000, 122, 8168-8179) describe ruthenium complexes which, as well as an N-heterocyclic carbene ligand, have an isopropoxybenzylidene ligand. These so-called “green” catalysts have a higher stability and can optionally be recycled.
The patent WO 9900397 describes catalysts C and D, which are particularly suitable for ROMP. The further examples of such highly active metathesis catalysts (E and F) are described in the application WO 2005094345.

Some examples of metathesis catalysts with sulphur-containing units in the side chain have been described in the literature (complex H in P. A. van der Schaaf et al. J. Organometallic Chem. 2000, 606, 65-74, complex J1 in Patent CN 2005100803792 and complex J2 in M. Bieniek et al. J. Organomet. Chem. 2006, 691, 5289).

Nevertheless, there was still a need for novel catalyst systems for olefin metathesis which are stable and additionally exhibit a high, possibly controllable activity and can be utilized as alternative catalysts to the existing catalysts. In particular, the catalysts, viewed as a whole, should be superior to the prior art catalysts viewed from the economic and/or ecological standpoint.